ATM协议介绍

H
...
ATM cell ATM cell
-
H
U U
Data ATM cell
T
VC-Based Multiplexing
•Each VC is configured and dedicated for a given
protocol •LLC/SNAP header is not required
IP VC 1 Netbeui VC 2 IPX VC 3 Source Destination
regress@olympus1# run show interfaces at-2/3/1
Physical interface: at-2/3/1, Enabled, Physical link is Up Interface index: 138, SNMP ifIndex: 31 Link-level type: ATM-PVC, MTU: 9192, Clocking: Internal, SONET mode, Speed: OC3, Loopback: None, Payload scrambler: Enabled Device flags : Present Running Link flags : None CoS queues : 8 supported, 4 maximum usable queues Current address: 00:19:e2:36:52:ba Last flapped : Never Input rate : 688 bps (4 pps) Output rate : 688 bps (4 pps) SONET alarms : None SONET defects : None VPI 0 Flags: Active Total down time: 0 sec, Last down: Never Traffic statistics: Input packets: 9 Output packets: 10 VPI 1 Flags: Active Total down time: 0 sec, Last down: Never Traffic statistics: Input packets: 3790 Output packets: 3842 VPI 2 Flags: Active Total down time: 0 sec, Last down: Never Traffic statistics: Input packets: 0 Output packets: 14 VPI 3 Flags: Active Total down time: 0 sec, Last down: Never Traffic statistics: Input packets: 3660 Output packets: 3660
VLAN header info. Is not transmitted
AA-AA-03
00-80-C2 00-07
00-00
L2 frame
OUI
LLC SNAP
PID
(2 byte padding)
(DMAC-SMAC-ethType-L3 data-FCS)
UUCPI length crc-32 (1) (1) (2) (4) (8 byte) AAL5 trailer
Control Plane
Version 3.0/3.1/4.0
Management Plane
Integrated Local Management Interface (ILMI)

User Plane Voice/Video/Data AAL (AAL1/AAL2/AAL5)
Control plane use ATM address before setting up an SVC; Mgmt. planes use ATM address for ILMI to learn about neighboring ATM switches
ATM cells
AAL2
Voice/Data from T1/E1 lines
Implemented in DSP
G.165/8 (ECAN), VAD
CODEC
SSCS
Features available in Upper layer of ATM protocol ref. model
AAL2
Pad UU CPI Len
CRC AAL5 packet
AAL5 trailer SNAP (OUI + PID) tells “Which L2 protocol is Bridged ” “Which L3 protocol is routed”
LLC/SNAP Routed packet looks like …
LLC/SNAP muxing RFC 1483/2684 VC Muxing
.
SMAC+DMAC+etype 8 bytes L2 Hdr Payload LLC SNAP
RFC 1483 or 2684
AA-AA-03 OUI (3 byte) (3 byte)
PID (2byte)
L3/L2 protocol Routed/Bridged packet `
Only padding & Trailer No header form AAL5
CPCS-PDU Payload (CPCS-SDU) <= 65,535 Octets
PAD 0-47 CPI Octets C
P
Length
CRC-32
In AAL5, SAR only does breaking/adding the payload into 48 C bytes, it does not add any header S
CPS Physical ATM
Sub cell muxing?
ATM cells
Subcell Muxing vs. No subcell Muxing
Virtual Circuit
Cell #1
Cell #2
Cell #1
CID = 8
CID = 9 CID = 8 & 9 Without subcell muxing With subcell muxing
• • • • • • • •
ATM Header
4
8
16
3
1
8
384 (48 bytes)
GFC
VPI
VCI
Payload CLP Type
HEC (CRC-8)
Payload
Inverse ARP
What is Cell delineation ?
PVC, SVC, SPVC
Idle cell VPI/VCI = 0/0 are transmitted when there is no traffic to sent; for ex: 120Mbps traffic is going thr. a 155Mbps OC3 pipe, remaining 30Mbps will be idle cells—use of idle cells for this purpose is called ―cell rate decoupling‖ Signaling 0/5 PNNI outing 0/18
PVC (0, 5) for PVC (0, 16) for ILMI Transmitting Signaling packets (SETUP…); VPI/VCI can also be different
PSTN TDM Network
STP
T1/E1 trunk
PBX
SS7 Network
Protocol call ref. Message Discrim Type
Message length
Responsible for signaling (UNI/PNNI) and QoS
Responsible for plane mgmt & OAM for layer mgmt-alarm generation
ATM
Sreenivas Naidu, IPG 25th March 2008
Topics for discussion
•
General intro on ATM * Header * Protocol stack * Few definitions Migration from PSTN to packet networks AAL1/AAL2 AAL5 * packet formats OAM Traffic classes Observations on Router show cli AAL5/ATM over MPLS Juniper supported implementations on AToM
Idle vs. Unassigned cell ILMI
ATM protocol stack
How QoS is supported? In SVC, Q.2931 message’s Info. Element
which AAL layer to use User cell rate, CBR/VBR; VPI/VCI values etc User side call state/network side call state Information Element (IE) variable length Setup/call proc/connect/ Connect-ACK/Release/Release-complete
ATM Heade r
…
1st ATM cell
ATM Heade r
Last ATM cell
Config: Vlan 10 int atm6/0/0.1.100 switchport mode access vlan 10 encap llc/snap
VC-MUX looks like …
IP packet or SDU from upper layers
SS7 A links
STP
SS7 Network
CAS/ PRI
TDM N/W
TDM Switch TDM Switch
PBX
AAL1 CES in PSTN network (trunking solution)
CAS/ PRI T1/E1 or T3/E3 PSTN ATM/IP Core Network
Q.2931 UNI Signaling
SSCF
AAL5
NULL for IP over ATM
SSCOP SSCS CPCS
AAL5
Also called Quasi Signaling AAL (QSAAL)
ATM layer Physical layer (SONET/SDH/T3/E3/T1)
LLC/SNAP Bridged packet looks like …
00-0E for BPDUs of STP
Bridged packet
This is an indication to the receiver that last 4 bytes FCS need to be stripped off or not before passing the data to the upper layers
CAS/ PRI
PSTN
ATM CES IWF
ATM CES IWF
AAL1 CES in enterprise applications (access solution)
CBR Service Interface (T1/E1)
PBX
ATM/IP Network
PBX
ATM CES IWF
ATM CES IWF
AAL1
Data from T1/E1 lines
Implemented in DSP
G.165/8 (ECAN) G.711 (PCM) CS
Features available in Upper layer of ATM protocol ref. model
AAL1
SAR Physical ATM
Routed packet Which L3 protocol AA-AA-03 00-00-00 OUI(3) LLC (3) SNAP 08-00 PID(2) L3 (IP packet/ARP) padding AAL5 trailer (8 byte)
Config: int atm6/0/0.1.100 ip address 20.1.1.1/24 encap llc/snap