D basic flows-routing-issues-vt00r00

ROUTING ISSUES IN BASIC CALL FLOWS DES
ROUTING ISSUES IN BASIC
CALL FLOWS
By: Daniel Esteban Soroko - 2011
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Contents
1 GENERAL INTRODUCTION: .................................................3
1.1 PURPOSE: .......................................................................................... 3
1.2 SCOPE:.............................................................................................. 3
1.3 ABBREVIATIONS AND TERMINOLOGY:.................................................... 3
1.4 REQUIRED INFORMATION: ................................................................... 3
1.5 RELATED DOCUMENTATION:................................................................. 3
2 OVERVIEW: ........................................................................4
2.1 EXAMPLE Nº1 (SIP TRAPEZOID WITHOUT USING RECORD-ROUTE AND
ROUTE): ..................................................................................................... 4
2.2 EXAMPLE Nº2 (SIP TRAPEZOID USING RECORD-ROUTE AND ROUTE): ...... 12
2.3 EXAMPLE Nº3 (SIP TRAPEZOID USING RECORD-ROUTE AND ROUTE -
VARIANT): ................................................................................................ 27
3 UA DIALOG STRUCTURES: ................................................39
3.1 FIELDS DESCRIPTION:....................................................................... 39
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1 GENERAL INTRODUCTION:
1.1 Purpose:
This document gives a brief detail of the mechanisms used to route SIP
messages and an approach about routing related header fields.
1.2 Scope:
This description depicts the routing mechanisms used in SIP messages.
1.3 Abbreviations and Terminology:
-.
1.4 Required information:
call_flow_woRR_v00.pdf: signalling flow example.
call_flow_w1RR_v00.pdf: signalling flow example.
call_flow_w2RR_v00.pdf: signalling flow example.
1.5 Related documentation:
RFC 3261: SIP: Session Initiation Protocol.
RFC 3263: Session Initiation Protocol (SIP): Locating SIP Servers.
RFC 3665: Session Initiation Protocol (SIP) Basic Call Flow Examples.
RFC 3666: Session Initiation Protocol (SIP) Public Switched Telephone
Network (PSTN) Call Flows.
RFC 5411: A Hitchhiker's Guide to the Session Initiation Protocol (SIP).
RFC 5627: Obtaining and Using Globally Routable User Agent URIs (GRUUs)
in the Session Initiation Protocol (SIP)
RFC 5630: The Use of the SIPS URI Scheme in the Session Initiation Protocol
(SIP).
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2 OVERVIEW:
In the next sections we will deal with SIP dialogs and routing of requests.
A Dialog is a peer-to-peer relationship between two user agents. It
represents a context that facilitates the sequencing of messages between the user
agents and proper routing of requests between both of them. The following
examples, illustrates the creation of a dialog, the processing of requests during this
dialog, and the termination of the dialog.
2.1 Example Nº1 (SIP trapezoid without using Record-Route and
Route):
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
This example shows two proxies in the routing path and neither of them
request to be maintained in the signalling path by inserting Record-Route header
fields. Only the header fields relevant to the dialog and the routing of requests are
shown in the SIP messages.
You can see the flow graph in “call_flow_woRR_v00.pdf” document. Next we
will describe each one of the flow’s messages and its relevant headers (“100
Trying” provisional response are ignored).
Note that we used the “blue” colour to denote FQDN identities, and
the “red” colour to denote NFQDN identities.
In this example “A” calls “B” using his SIP identity, a type of Uniform
Resource Identifier (URI) called a SIP URI. This SIP URI has a similar form to an
email address, typically containing a username and a host name. In this case, it is
“sip:bob@biloxi.com”, where “biloxi.com” is the domain of Bob's SIP service
provider. Alice has a SIP URI of “sip:alice@atlanta.com”.
Note than “sip:bob@biloxi.com” and “sip:alice@atlanta.com” are
logical identities that define the users, and “pc33.atlanta.com” and
“term24.biloxi.com”, are the physical identities (machines) where these
users reside. In the same way “bigbox3.site3.atlanta.com” and
“server10.biloxi.com”, are the proxies’ physical identities.
Note than “Request-URI” is part of the “Request-Line = Method SP
Request-URI SP SIP-Version CRLF”. Example: INVITE sip:bob@biloxi.com
SIP/2.0
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2.1.1-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
-“A” generates the INVITE request (Since the “A” softphone does not know the
location of Bob or the SIP server in the “biloxi.com” domain, the softphone sends
the INVITE to the SIP server that serves Alice's domain, “atlanta.com”. The address
of the “atlanta.com” SIP server could have been configured in Alice's softphone (as
an outbound proxy), or it could have been discovered by DHCP/DNS, for example).
M1
INVITE sip:bob@biloxi.com SIP/2.0
Via: SIP/2.0/UDP pc33.atlanta.com;branch=z9hG4bKnashds8
Max-Forwards: 70
To: Bob <sip:bob@biloxi.com>
From: Alice <sip:alice@atlanta.com>;tag=1928301774
Call-ID: a84b4c76e66710
CSeq: 314159 INVITE
Contact: <sip:alice@pc33.atlanta.com>
Header’s commentaries:
Request-URI: contains a SIP or SIPS URI (sip:bob@biloxi.com) that indicates the
user or service to which this request is being addressed.
Via: contains the address (pc33.atlanta.com) at which “A” is expecting to receive
responses to this request.
To: contains a SIP or SIPS URI (sip:bob@biloxi.com) towards which the request
was originally directed.
From: also contains a SIP or SIPS URI (sip:alice@atlanta.com) that indicate the
originator of the request.
Contact: contains a SIP or SIPS URI (sip:alice@pc33.atlanta.com) that represents a
direct route to contact Alice, usually composed of a username at a fully qualified
domain name (FQDN). While an FQDN is preferred, many end systems do not have
registered domain names, so IP addresses are permitted. While the Via header
field tells other elements where to send the response, the Contact header
field tells other elements where to send future requests.
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2.1.2-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
-“P1” inspects the received “Request-URI” in M1 message (sip:bob@biloxi.com) and
does not change it because it is not responsible for the resource indicated in this
URI.
-“P1” forwards the request to the resource indicated in the “Request-URI”
(sip:bob@biloxi.com) by applying DHCP/DNS procedures.
M2
Via: SIP/2.0/UDP bigbox3.site3.atlanta.com;branch=z9hG4bK77ef4c2312983.1
Via: SIP/2.0/UDP pc33.atlanta.com;branch=z9hG4bKnashds8;received=192.0.2.1
Max-Forwards: 69
CSeq: 314159 INVITE
Via: P1 adds its own via header in the routing path (bigbox3.site3.atlanta.com), for
its use in the response messages.
2.1.3-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
-“P2” inspects the received “Request-URI” in M2 message (sip:bob@biloxi.com). It
is responsible for “biloxi.com”, so it runs a location service and rewrites the
“Request-URI” (sip:bob@biloxi.com -> sip:bob@term24.biloxi.com)
-“P2” forwards the request to the resource indicated in the “Request-URI” (sip:
bob@term24.biloxi.com) by applying DHCP/DNS procedures.
M4
INVITE sip:bob@term24.biloxi.com SIP/2.0
Via: SIP/2.0/UDP server10.biloxi.com;branch=z9hG4bK4b43c2ff8.1
Via: SIP/2.0/UDP
bigbox3.site3.atlanta.com;branch=z9hG4bK77ef4c2312983.1;received=192.0.2.2
Max-Forwards: 68
CSeq: 314159 INVITE
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Via: P2 adds its own via header in the routing path (server10.biloxi.com), for its
use in the response messages.
2.1.4-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
-“B” inspects the received message (M4). Then it stores the “A” “Contact header”
(alice@pc33.atlanta.com) in its UA “dialog data structure” as “Remote Target”. It
uses the “Request-URI” of M4 to fill its own “Contact” header.
-“B” creates the 180 response message.
-“B” sends the 180 response message by using the “Via” headers.
M6
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP server10.biloxi.com;branch=z9hG4bK4b43c2ff8.1;received=192.0.2.3
Via: SIP/2.0/UDP bigbox3.site3.atlanta.com;
branch=z9hG4bK77ef4c2312983.1;received=192.0.2.2
To: Bob <sip:bob@biloxi.com>;tag=a6c85cf
Contact: <sip:bob@term24.biloxi.com>
CSeq: 314159 INVITE
Contact: “B” adds a Contact header field to the response, with its direct route
(sip:bob@term24.biloxi.com). “B” obtain this value from the Request-URI of the
incoming request (M4).
To: “B” adds its local tag, to “To” header.
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2.1.5-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
-“P2” forwards the 180 response message by using the “Via” headers.
M7
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP
CSeq: 314159 INVITE
Via: P2 delete its own via header in the routing path (server10.biloxi.com).
2.1.6-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
M8
SIP/2.0 180 Ringing
CSeq: 314159 INVITE
Via: P1 delete its own via header in the routing path (bigbox3.site3.atlanta.com).
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2.1.7-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
M9
SIP/2.0 200 OK
Via: SIP/2.0/UDP
CSeq: 314159 INVITE
(sip:bob@term24.biloxi.com). “B” obtains this value from the Request-URI of the
2.1.8-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
M10
SIP/2.0 200 OK
Via: SIP/2.0/UDP bigbox3.site3.atlanta.com;branch=z9hG4bK77ef4c2312983.1 ;
received=192.0.2.2
CSeq: 314159 INVITE
Via: P2 delete its own via header in the routing path (server10.biloxi.com).
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2.1.9-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
M11
SIP/2.0 200 OK
CSeq: 314159 INVITE
Via: P1 delete its own via header in the routing path (bigbox3.site3.atlanta.com).
2.1.10-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
-“A” inspects the received message (M11). Then it stores the “B” “Contact header”
in its UA “dialog data structure” as “Remote Target”.
-“A” creates the ACK request.
-“A” sends the ACK request by using the Contact header received in
M11(bob@term24.biloxi.com).
M12
ACK sip:bob@term24.biloxi.com SIP/2.0
Max-Forwards: 70
CSeq: 314159 ACK
Request-URI: contains a SIP or SIPS URI (sip:bob@term24.biloxi.com) that
indicates the user or service to which this request is being addressed.”A” fills it
value, with the received “Contact” header of M11 message.
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2.1.11-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
-“B” creates a BYE message.
-“B” sends the BYE request by using the “Remote Target” of UA dialog data
structure (alice@pc33.atlanta.com) (see 2.1.4-).
M13
BYE sip:alice@pc33.atlanta.com SIP/2.0
Via: SIP/2.0/UDP term24.biloxi.com;branch=z9hG4bKnashds10
Max-Forwards: 70
From: Bob <sip:bob@biloxi.com>;tag=a6c85cf
To: Alice <sip:alice@atlanta.com>;tag=1928301774
CSeq: 231 BYE
Request-URI: “B” fills the Request-URI value, “Remote Target” of UA dialog data
structure
(alice@pc33.atlanta.com) (see 2.1.4-).
2.1.12-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|-----------------M12(ACK)--------------->|
|<----------------M13(BYE)----------------|
|-----------------M14(200)--------------->|
-“A” creates a 200 OK response to respond to the BYE message.
-“A” sends the 200 response by using the “Via headers”.
M14
SIP/2.0 200 OK
CSeq: 231 BYE
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2.2 Example Nº2 (SIP trapezoid using Record-Route and Route):
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
This example shows two proxies in the routing path and both of them
You can see the flow graph in “call_flow_w2RR_v00.pdf” document. Next we
SIP/2.0
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2.2.1-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
M1
Max-Forwards: 70
CSeq: 314159 INVITE
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2.2.2-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
URI.
-“P1” adds a Record-Route header with its own address
(bigbox3.site3.atlanta.com). (The next requests must traverse this address).
M2
Max-Forwards: 69
CSeq: 314159 INVITE
Record-Route: sip:bigbox3.site3.atlanta.com;lr>
Via: “P1” adds its own “Via” header in the routing path (bigbox3.site3.atlanta.com),
for its use in the response messages.
Record-Route: “P1” adds a “Record-Route” header with its own
address(bigbox3.site3.atlanta.com). (The next requests must traverse this
address).
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2.2.3-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
-“P2” adds a Record-Route header with its own address (server10.biloxi.com). (The
next requests must traverse this address).
M4
Via: SIP/2.0/UDP
Max-Forwards: 68
CSeq: 314159 INVITE
Record-Route: sip:server10.biloxi.com;lr>
Via: P2 adds its own “Via” header in the routing path (server10.biloxi.com), for its
Record-Route: “P2” adds a “Record-Route” header with its own address
(server10.biloxi.com). (The next requests must traverse this address).
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2.2.4-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
-“B” inspects the received message (M4). Then it stores:
The “A” “Contact” header in its UA “dialog data structure” as “Remote
Target”
(alice@pc33.atlanta.com).
The “Record-Route” headers in its UA “dialog data structure” as “Route Set”.
(server10.biloxi.com; bigbox3.site3.atlanta.com)
-“B” uses the “Request-URI” (bob@term24.biloxi.com) of M4 to fill its own
“Contact” header.
-“B” copies all the Record-Route headers to the 180 response message.
M6
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP bigbox3.site3.atlanta.com; branch=z9hG4bK77ef4c2312983.1
;received=192.0.2.2
CSeq: 314159 INVITE
Contact: “B” adds a “Contact” header field to the response, with its direct route
Record-Route: “B” copies the received “Record-Route” headers into the response
message.
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2.2.5-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
M7
SIP/2.0 180 Ringing
;received=192.0.2.2
CSeq: 314159 INVITE
Via: P2 delete its own “Via” header in the routing path (server10.biloxi.com).
2.2.6-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
M8
SIP/2.0 180 Ringing
CSeq: 314159 INVITE
Via: P1 delete its own “Via” header in the routing path (bigbox3.site3.atlanta.com).
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2.2.7-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
M9
SIP/2.0 200 OK
Via: SIP/2.0/UDP
CSeq: 314159 INVITE
message.
2.2.8-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
M10
SIP/2.0 200 OK
Via: SIP/2.0/UDP
CSeq: 314159 INVITE
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2.2.9-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
M11
SIP/2.0 200 OK
CSeq: 314159 INVITE
Via: P1 delete its own via “Via” header in the routing path
(bigbox3.site3.atlanta.com).
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2.2.10-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
-“A” inspects the received message (M11). Then it stores :
The “B” “Contact” header (bob@term24.biloxi.com) in its UA “dialog data
structure” as “Remote Target”.
The “Record-Route” headers in its UA “dialog data structure” as “Route Set”
(bigbox3.site3.atlanta.com ; server10.biloxi.com).
-“A” adds the “Route” headers using the stored “Route Set”
-“A” sends the ACK request by using the first value of “Route Set”.
(bigbox3.site3.atlanta.com ; server10.biloxi.com)
M12
Max-Forwards: 70
CSeq: 314159 ACK
Route:sip:bigbox3.site3.atlanta.com
Route:sip:server10.biloxi.com
Request-URI: “A” fills the Request-URI value, with “Remote Target” value of UA
dialog data structure (bob@term24.biloxi.com).
Route: contains the addresses that they will used to route the message. (Its value
was the previously recorded “Route Set”) (bigbox3.site3.atlanta.com ;
server10.biloxi.com).
DES Page :20/40

2.2.11-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
-“P1” inspects the Request-URI of the received message (M12), and does not
change it because is not responsible for the resource indicated in this URI.
-“P1” sees that it is the first value in the “Route” header field so it removes that
value (sip:bigbox3.site3.atlanta.com).
-“P1” forwards the request to the resource indicated in the topmost “Route” header
(sip:server10.biloxi.com) field applying DHCP/DNS procedures.
M13
Max-Forwards: 69
CSeq: 314159 ACK
Via: P1 adds its own “Via” header in the routing path (bigbox3.site3.atlanta.com).
Route: P1 delete its own “Route” header in the routing path
DES Page :21/40

2.2.12-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
change it because is not responsible for the resource indicated in this URI (it is
responsible for “biloxi.com”, not “term24.biloxi.com”).
value (sip: server10.biloxi.com).
-“P2” forwards the request to the resourse indicated in the Request-URI
(sip:bob@term24.biloxi.com) because there are not more “Route” headers,
applying DHCP/DNS procedures.
M14
Max-Forwards: 68
CSeq: 314159 ACK
Via: P2 adds its own “Via” header in the routing path (server10.biloxi.com).
Route: P2 delete its own “Route” header in the routing path (server10.biloxi.com).
DES Page :22/40

2.2.13-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
-“B” adds “Route” headers using the data stored at “Route Set”
(server10.biloxi.com; bigbox3.site3.atlanta.com) (see 2.2.4-).
-“B” sets “Request-URI” header using the data stored at “Remote
Target”(alice@pc33.atlanta.com) (see 2.2.4-).
-“B” sends the ACK request by using the first value of “Route Set”.
(server10.biloxi.com ; bigbox3.site3.atlanta.com)
M15
Max-Forwards: 70
CSeq: 231 BYE
Route: sip:server10.biloxi.com
Route: sip:bigbox3.site3.atlanta.com
Request-URI: “B” fills the Request-URI value, with “Remote Target” value of UA
dialog data structure (alice@pc33.atlanta.com) (see 4-).
was the previously recorded “Route Set”) (server10.biloxi.com ;
bigbox3.site3.atlanta.com).
DES Page :23/40

2.2.14-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
change it because is not responsible for the resource indicated in this URI..
-“P2” forwards the request to the resource indicated in the topmost “Route” header
(sip: bigbox3.site3.atlanta.com) field applying DHCP/DNS procedures.
M16
Max-Forwards: 69
CSeq: 231 BYE
Route: sip:bigbox3.site3.atlanta.com
(server10.biloxi.com).
DES Page :24/40

2.2.15-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
change it because is not responsible for the resource indicated in this URI URI (it is
responsible for “atlanta.com”, not “pc33.atlanta.com”).
value (sip: bigbox3.site3.atlanta.com).
(sip:alice@pc33.atlanta.com) because there are not more “Route” headers,
M17
Via: SIP/2.0/UDP bigbox3.site3.atlanta.com;
branch=z9hG4bK77ef4c2312983.1
Max-Forwards: 68
CSeq: 231 BYE
Via: P1 adds its own “Via” header in the routing path
2.2.16-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
M18
SIP/2.0 200 OK
CSeq: 231 BYE
DES Page :25/40

2.2.17-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
-“P1” forwards the 200 response by using the “Via” header field.
M19
SIP/2.0 200 OK
CSeq: 231 BYE
Via: P1 deletes its own “Via” header in the routing path
2.2.18-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---M12(ACK)->|---M13(ACK)->|---M14(ACK)->|
|<--M17(BYE)--|<--M16(BYE)--|<--M15(BYE)--|
|---M18(200)->|---M19(200)->|---M20(200)->|
M20
SIP/2.0 200 OK
CSeq: 231 BYE
DES Page :26/40

2.3 Example Nº3 (SIP trapezoid using Record-Route and Route -
Variant):
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
This example shows two proxies in the routing path and neither of them
You can see the flow graph in “call_flow_w1RR_v00.pdf” document. Next we
SIP/2.0
DES Page :27/40

2.3.1-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
M1
Max-Forwards: 70
CSeq: 314159 INVITE
DES Page :28/40

2.3.2-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
URI.
M2
Max-Forwards: 69
CSeq: 314159 INVITE
Via: “P1” adds its own “Via” header in the routing path (bigbox3.site3.atlanta.com),
for its use in the response messages.
DES Page :29/40

2.3.3-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
-“P2” adds a Record-Route header with its own address (server10.biloxi.com). (The
next requests must traverse this address).
M4
Via: SIP/2.0/UDP
Max-Forwards: 68
CSeq: 314159 INVITE
Via: P2 adds its own “Via” header in the routing path (server10.biloxi.com), for its
Record-Route: “P2” adds a “Record-Route” header with its own address
(server10.biloxi.com). (The next requests must traverse this address).
DES Page :30/40

2.3.4-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
-“B” inspects the received message (M4). Then it stores:
The “A” “Contact” header in its UA “dialog data structure” as “Remote
Target” (alice@pc33.atlanta.com).
The “Record-Route” headers in its UA “dialog data structure” as “Route Set”.
(server10.biloxi.com)
-“B” uses the “Request-URI” (bob@term24.biloxi.com) of M4 to fill its own
“Contact” header.
-“B” copies all the Record-Route headers to the 180 response message.
M6
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP bigbox3.site3.atlanta.com; branch=z9hG4bK77ef4c2312983.1
;received=192.0.2.2
CSeq: 314159 INVITE
Contact: “B” adds a “Contact” header field to the response, with its direct route
message.
DES Page :31/40

2.3.5-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
M7
SIP/2.0 180 Ringing
;received=192.0.2.2
CSeq: 314159 INVITE
2.3.6-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
M8
SIP/2.0 180 Ringing
CSeq: 314159 INVITE
Via: P1 delete its own “Via” header in the routing path (bigbox3.site3.atlanta.com).
DES Page :32/40

2.3.7-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
M9
SIP/2.0 200 OK
Via: SIP/2.0/UDP
CSeq: 314159 INVITE
(sip:bob@term24.biloxi.com). “B” obtains this value from the Request-URI of the
message.
2.3.8-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
M10
SIP/2.0 200 OK
Via: SIP/2.0/UDP
CSeq: 314159 INVITE
DES Page :33/40

2.3.9-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
M11
SIP/2.0 200 OK
CSeq: 314159 INVITE
Via: P1 delete its own via “Via” header in the routing path
2.3.10-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
-“A” inspects the received message (M11). Then it stores :
The “B” “Contact” header (bob@term24.biloxi.com) in its UA “dialog data
structure” as “Remote Target”.
The “Record-Route” headers in its UA “dialog data structure” as “Route Set”
-“A” adds the “Route” headers using the stored “Route Set” (server10.biloxi.com).
-“A” sends the ACK request by using the unique value of “Route Set”
M12
Max-Forwards: 70
CSeq: 314159 ACK
DES Page :34/40

Request-URI: “A” fills the Request-URI value, with “Remote Target” value of UA
dialog data structure (bob@term24.biloxi.com) (see 2.3.4-).
was the previously recorded “Route Set”) (server10.biloxi.com) (see 2.3.4-).
2.3.11-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
change it because is not responsible for the resource indicated in this URI (it is
responsible for “biloxi.com”, not “term24.biloxi.com”).
(sip:bob@term24.biloxi.com) because there are not more “Route” headers,
M13
Max-Forwards: 69
CSeq: 314159 ACK
Route: P2 delete its own “Route” header in the routing path (server10.biloxi.com).
DES Page :35/40

2.3.12-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
-“B” adds “Route” headers using the data stored at “Route Set”
(server10.biloxi.com) (see 2.3.4-).
-“B” sets “Request-URI” header using the data stored at “Remote
Target”(alice@pc33.atlanta.com) (see 2.3.4-).
-“B” sends the ACK request by using the first value of “Route Set”.
(server10.biloxi.com)
M14
Max-Forwards: 70
CSeq: 231 BYE
Route: sip:server10.biloxi.com
Request-URI: “B” fills the Request-URI value, with “Remote Target” value of UA
dialog data structure (alice@pc33.atlanta.com) (see 2.3.4-).
was the previously recorded “Route Set”) (server10.biloxi.com).
DES Page :36/40

2.2.13-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
change it because is not responsible for the resource indicated in this URI..
(sip:alice@pc33.atlanta.com) because there are not more “Route” headers,
M15
Max-Forwards: 69
CSeq: 231 BYE
2.3.14-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
M16
SIP/2.0 200 OK
CSeq: 231 BYE
DES Page :37/40

2.3.15-
A P1 P2 B
|---M1(INV)-->|---M2(INV)-->|---M4(INV)-->|
|<--M8(180)---|<--M7(180)---|<--M6(180)---|
|<--M11(200)--|<--M10(200)--|<--M9(200)---|
|---------M12(ACK)--------->|---M13(ACK)->|
|<--------M15(BYE)----------|<--M14(BYE)--|
|---------M16(200)--------->|---M17(200)->|
M20
SIP/2.0 200 OK
CSeq: 231 BYE
DES Page :38/40

3 UA DIALOG STRUCTURES:
In the UA there are data structures that are used to store dialogues’ states
and necessary parameters for the interchange of messages. In the previous
sections, we mentioned some of these parameters. In this section we will
enumerate these parameters.
This data structures are not standarised, but through its use on “best
practices” they became in a defacto design standard.
Figure Nº1: UA dialog structure
Note than exists a field named “Other parameters”, in this field I grouped
some existing fields, that I will mention briefly.
3.1 Fields description:
Each UA can behave like UAS or UAC for different dialogues. One UA will
behave like UAC if it sends requests in a certain dialog and one UA will behave like
UAS if it sends responses in a certain dialog. Some of the fields of the UA dialog
structure take its value in different form if the UA acts as an UAC or an UAS.
Figure Nº2: UAC-UAS scheme.
In the following lines I will give a description of the structure’s fields.
Between square brackets will be added the related SIP header in each case.
Call-Id [Call-Id]: This field stores de Call-ID of the call. A generated Call-Id for UAC
(see 2.1.1) or a received Call-ID for UAS (see 2.1.4).
Local Tag [From(UAC);To(UAS)]: This field stores the generated local tag used in
the “From” header in the UAC (see 2.1.1) or the generated local tag for the “To”
header in the UAS (see 2.1.4).
DES Page :39/40

Remote Tag [To(UAC);From(UAS)]: This field stores the received tag in the “From”
header in the UAC (see 2.1.6 - “A” node) or the received tag in the “To” header in
the UAS (see 2.1.4).
Local seqnum[Cseq(UAC)]: This field stores the generated Cseq for UAC (see
2.1.1).
Remote seqnum[Cseq(UAS)]: This field stores the received Cseq for UAS (see
2.1.4).
Local URI [From(UAC);To(UAS)]: This field stores the local URI used in the “From”
header in the UAC (see 2.1.1) or in the “To” header in the UAS (see 2.1.4).
Remote URI [To(UAC); From(UAS); Request-URI(UAC*)]: This field stores the
remote URI used in the “To” header in the UAC (see 2.1.1) or in the “To” header in
the UAS (see 2.1.4). Under certain conditions this value is used on “Request-URI”
by UAC (see 2.1.1 [Condition: In the first INVITE of an outgoing call]).
Local target [Contact]: This field stores the value for “Contact” header. This value is
generated on UAC (see 2.1.1) or obtained from “Request-URI” in UAS(see
2.1.4)/UAC only under certain conditions.
Remote target [Request-URI]: This field stores the value for “Request-URI” header.
This value is obtained from “Contact” header in UAS(see 2.1.4)/UAC(see 2.1.6 node
“A”) or generated in UAC under certain conditions.
Route Set[Record-Route, Route]: This field stores the values obtained from
“Record-Route” headers and used in “Route” headers.(see 2.2.6 node “A” , see
2.2.4).
Secure flag: This field stores when the UA uses TLS for signalling or SRTP for audio
streams.
Other parameters: “display” part, “P-Preferred-Identity”,”A-Asserted-
Identity”,”Privacy”. The mentioned headers are related to the “local tag”
identification through public networks. The values that they can take depend on the
country network “id” parameters and interconnection terms.
DES Page :40/40

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