This chapter is definitely more informative than the last one.  Anyways, here are some my notes.

MPLS Fundamentals - Chapter 5: MPLS and ATM Architecture

ATM Cell Format
-I.361 Layer
-Header - 5 bytes
-Payload - 48 bytes
-UNI Header - Contains 4 bits of Generic Flow Control (GFC)
-NNI Header - No GFC, ATM switches use 4 bits for VPI; contains Data/Mgmt, EFCI, and M-bit

AAL
-Layer between ATM and upper layer
-5 Categories
–AAL1 - connection-oriented; used for delay-sensitive services and circuit emulation
–AAL2 - connection-oriented; used for variable rate services
–AAL3/4 - connectionless; used for SMDS
–AAL5 - connection-oriented or connectionless; used for varying bit rate demands

Overlay Network
-Routers need to be interconnected in a full mesh and use an IGP for peering

Peer Model
-Routers are now edge LSRs connected without IGP adjacency
-MPLS encapsulated
-MPLS label value is mapped to VPI/VCI

Label Encoding
-Only top label is mapped to VPI/VCI
-Label stack is set to 0

Label Advertisement
-IGP and LDP cannot run directly over ATM interface and establish a neighborship; a control VC is needed
-Label Switched Controlled Virtual Circuit (LVC)
–Configure ATM interfaces to be Label Switching Controlled-ATM (LC-ATM) interfaces
–Encapsulation must be LLC/SNAP
-Tag Switching Controlled Virtual Circuit (TVC)

Downstream-on-Demand Label Advertisement
-ATM LSR only advertises a label when it is requested
-ATM LSRs use the Ordered LSP Control mode whereas non-LC-ATM routers use the Independent LSP Control mode
-Downstream ATM LSR only replies with a label if it has received a label for the prefix

ATM Switch Position
-Tail End Switch - means ATM LSR is egress
-Transit - ATM LSR between ingress and egress on the LSP
-Head End Switch - means ATM LSR is ingress

LDP Control Mode
-Independent - means an LSR immediately responds to a Label Request message from upstream
-Ordered - means that LSR only responds to the Label Request message from upstream when it received a response its Label Request message from its downstream LSR
-Ordered is default in IOS

Label Space
-Per-inteface label space is used for LC-ATM

Aggregate Labels
-Avoid aggregating labels on ATM LSRs when labeled packets must become unlabeled; serious performance impact

Non MPLS-Aware ATM Switches
-Run VP tunnels across the non-MPLS-aware ATM switches that will carry LVCs

Methods for reducing LVCs
-Reduce IP prefixes - Use a loopback and IP unnumbered
-VC-Merge - Reduces one VC per destination regardless of the number of upstream neighbors
-Map CoS classes - Map several classes to one Multi-VC TBR LVC type: available, standard, premium, and control
-Disable head end VCs - ATM LSR cannot function as edge ATM LSR
-Block Label Request - Blocks the signaling of the VCs

For me, returning back to work after a long weekend is a slow process.  I find that I need to spark my motivation in some way, so before diving in to my workload, I decided to read up on MPLS.  The main reason for reading up on MPLS (and not something else more enjoyable) was to prepare for a proposal that I needed to write up for a client.  Since terminology is often thrown around in meetings and discussions, I figured during my morning lull that it was best to solidify my knowledge of the technology.  I pretty much read through Chapters 1 & 2 fairly quickly.  Based on past experiences, the bulk of the material for Cisco Press books seems to appear in the 3rd chapter.  On that point, here are the notes I gathered:

MPLS Fundamentals - Chapter 3: Forwarding Labeled Packets

IP Lookup vs Label Lookup
-Lookup in CEF table
–IP-to-IP
–IP-to-label
-Lookup in LFIB table
–Label-to-IP
–Label-to-label

Label Operations Recap
-Pop - top label is removed; packet forwarded with remaining label stack or as an unlabeled packet
-Swap - top label is removed and replaced with a new label
-Push - top label is replaced with new label (swapped) and one or more labels are added (pushed) on top of the swapped label
-Untagged/No label - stack is removed and packet is forwarded unlabeled
-Aggregate - label stack is removed and IP lookup is performed on IP packet

Unknown Label
-LSR will drop incoming packets with an unknown top label

Reserved Labels 0 - 15
-0 - Explicit NULL Label - Maintains QoS on PHP
-1 - Router Alert Label - Present anywhere in stack except bottom; packet not forwarded in hardware will be reviewed by software process
-2 - IPv6 Explicit NULL Label
-3 - Implicit NULL Label - PHP; removes LFIB lookup for directly connected and summary
-14 - OAM Alert Label - Not used by IOS; used for failure detection, localization, and performance monitoring

IP TTL
-An 8-bit field within an IP header signifies the time a packet has to live before it is dropped;  TTL is usually 255 and decremented by 1 at each hop; When TTL reaches 0, packet is dropped by router and sends ICMP message type 11, code 0 (time exceeded) to end of LSP for delivery to originator (i.e. P-router has no knowledge of orignator routes)

MPLS TTL
-IP TTL value is copied to pushed labels
–IP-to-MPLS Behavior of MPLS TTL - Safeguard mechanism in IOS does not copy if MPLS TTL > IP TTL
–Label-to-label Behavior of MPLS TTL - Swap operation, TTL of incoming label -1 is copied to swapped label; Push operation, received MPLS TTL of top label -1 is copied to swapped and pushed labeles; Pop operation, TTL of incoming label -1 is copied to new exposed label
–P-router Behavior of MPLS TTL - Notes what the MPLS payload, a Layer 2 frame, is when the TTL expires; drops packets if not IPv4 or IPv6

MPLS MTU
-n * 4 bytes, n = # of labels
-sh mpls int det
-mpls mtu ‘1500 + (2 * 4)’
-Giant Frame
–Layer 2 frame that reaches max size for data link
-Baby Giant Frame
–Slightly bigger than max allowed
–Recommended on switches
—system jumbomtu
—system mtu
—mtu (int setting)

MPLS MRU
-Cisco proprietary; LSR is informed how big a received label packet of a certain FEC that can still be forwarded out without fragmentation; label operation determines MRU per FEC or prefix

Fragmentation
-If labeled packet exceeds outgoing MTU, the LSR strips the label stack and fragments IP; if DF-bit set, ICMP error message type 3, code 4 (Fragmentation needed and do not fragment bit set) is sent to end of LSP
-Path MTU Discovery - Orignator that receives ICMP error message type 3, code 4 lowers the size of packet and retransmits to avoid fragmentation
–Firewalls, ACLs, and routing issues can prohibit originator receipt of ICMP error message type 3, code 4